LIDAR sensor system with small form factor

ABSTRACT

A sensor system can comprise a light source generating a light pulse that is collimated, and a plurality of optical elements. Each of the plurality of optical elements is configured to rotate independently about an axis that is substantially common, and the plurality of optical elements operate to collectively direct the light pulse to one or more objects in an angle of view of the sensor system. Furthermore, the sensor system can comprise a detector configured to receive, via the plurality of optical elements, at least a portion of photon energy of the light pulse that is reflected back from the one or more objects in the angle of view of the sensor system, and convert the received photon energy into at least one electrical signal.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/729,551, filed Oct. 10, 2017, which is a continuation ofInternational Patent Application No. PCT/CN17/078611, filed Mar. 29,2017, all of which are incorporated herein by reference.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

FIELD OF THE INVENTION

The disclosed embodiments relate generally to optical sensing, and moreparticularly, but not exclusively, to optical scanning and ranging.

BACKGROUND

Sensors are important for performing various types of operations, e.g.by movable or stationary objects. Especially, movable objects, such asrobots, manned vehicles and unmanned vehicles, can take advantage ofdifferent sensors for navigating in a complex environment. For example,movable objects need to be aware of surrounding condition in order forperforming path planning and obstacle detection and avoidance in anunknown environment. This is the general area that embodiments of theinvention are intended to address.

SUMMARY

Described herein are systems and methods that provide a technicalsolution for performing optical detection and ranging. A sensor systemcan comprise a light source generating a light pulse that is collimated,and a plurality of optical elements. Each of the plurality of opticalelements is configured to rotate independently about an axis that issubstantially common, and the plurality of optical elements operate tocollectively direct the light pulse to one or more objects in an angleof view of the sensor system. Furthermore, the sensor system cancomprise a detector configured to receive, via the plurality of opticalelements, at least a portion of photon energy of the light pulse that isreflected back from the one or more objects in the angle of view of thesensor system, and convert the received photon energy into at least oneelectrical signal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic diagram of an exemplary LIDAR sensing system,in accordance with various embodiments of the present invention.

FIG. 2 shows a schematic diagram of an exemplary LIDAR sensor systemusing a Risley prism pair, in accordance with various embodiments of thepresent invention.

FIG. 3 shows an exemplary refraction model for using a Risley prismpair, in accordance with various embodiments of the present invention.

FIG. 4 shows an exemplary illustration of rotating prisms in a LIDARsensor system, in accordance with various embodiments of the presentinvention.

FIG. 5 shows the configuration of an exemplary LIDAR sensor system usinga beam splitter, in accordance with various embodiments of the presentinvention.

FIG. 6 shows an alternative exemplary LIDAR sensing scheme, inaccordance with various embodiments of the present invention.

FIG. 7 shows an exemplary illustration of an alternative LIDAR sensorsystem, in accordance with various embodiments of the present invention.

FIG. 8 shows an exemplary illustration of a LIDAR sensor system withdifferent light emitting configurations, in accordance with variousembodiments of the present invention.

FIG. 9 shows an exemplary illustration of optimizing a light emittingstructure in a LIDAR sensor system, in accordance with variousembodiments of the present invention.

FIG. 10 shows a schematic diagram of preventing optical contamination inan exemplary LIDAR sensor system, in accordance with various embodimentsof the present invention.

FIG. 11 shows a schematic diagrams of creating a band-pass filter withnarrow passing band, in accordance with various embodiments of thepresent invention.

FIG. 12 shows a schematic diagram of spatial filtering in an exemplaryLIDAR system, in accordance with various embodiments of the presentinvention.

FIG. 13 shows schematic diagrams of using alternative approaches forproviding spatial filtering in an exemplary LIDAR sensor system, inaccordance with various embodiments of the present invention.

FIG. 14 shows a schematic diagram of using a field stop aperture (FSA)in an exemplary LIDAR sensor system, in accordance with variousembodiments of the present invention.

FIG. 15 shows an exemplary configuration of a LIDAR sensor system thatcan reduce undesired back-reflection, in accordance with variousembodiments of the present invention.

FIG. 16 shows a flowchart of sensing using a LIDAR sensor system, inaccordance with various embodiments of the present invention.

FIG. 17 shows an exemplary illustration of controlling a LIDAR sensorsystem, in accordance with various embodiments of the present invention.

FIG. 18 shows an exemplary illustration of a deviation model forrotating a Risley prism pair, in accordance with various embodiments ofthe present invention.

FIG. 19 shows exemplary illustration of different scanning patternsusing a LIDAR sensor system, in accordance with various embodiments ofthe present invention.

FIG. 20 shows exemplary illustration of a uniform scanning pattern usinga LIDAR sensor system, in accordance with various embodiments of thepresent invention.

FIG. 21 shows an exemplary illustration of controlling beam steering fora LIDAR sensor system, in accordance with various embodiments of thepresent invention.

FIG. 22 shows an exemplary illustration of alternative LIDAR sensorsystems, in accordance with various embodiments of the presentinvention.

FIG. 23 shows an exemplary illustration of mounting a LIDAR sensorsystem on various movable platforms, in accordance with variousembodiments of the present invention.

FIG. 24 shows an exemplary illustration of using a LIDAR sensor systemto perform three dimensional scan, in accordance with variousembodiments of the present invention.

FIG. 25 shows an exemplary illustration of combining multiple LIDARsensor systems, in accordance with various embodiments of the presentinvention.

FIG. 26 shows a flowchart of scanning using a LIDAR sensor system, inaccordance with various embodiments of the present invention.

DETAILED DESCRIPTION

The invention is illustrated, by way of example and not by way oflimitation, in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” or “some” embodiment(s) in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone.

The description of the invention as following uses a light detection andranging (LIDAR) sensor system as example for a sensor system. It will beapparent to those skilled in the art that other types of sensor systemscan be used without limitation.

In accordance with various embodiments, a technical solution can beprovided for performing optical detection and ranging. A sensor systemcan comprise a light source generating a light pulse that is collimated,and a plurality of optical elements. Each of the plurality of opticalelements is configured to rotate independently about an axis that issubstantially common, and the plurality of optical elements operate tocollectively direct the light pulse to one or more objects in an angleof view of the sensor system. Furthermore, the sensor system cancomprise a detector configured to receive, via the plurality of opticalelements, at least a portion of photon energy of the light pulse that isreflected back from the one or more objects in the angle of view of thesensor system, and convert the received photon energy into at least oneelectrical signal.

In accordance with various embodiments, a technical solution can beprovided for performing optical detection and ranging. A sensor systemcan comprise a light source that operates to generate a series of lightpulses at different time points, and a plurality of optical elements,wherein each of the plurality of optical elements is configured torotate independently about an axis that is substantially common.Furthermore, the sensor system can comprise a controller that operatesto control respective rotation of each of the plurality of opticalelements, in order to collectively direct the series of light pulses todifferent directions in an angle of view of the sensor system, and adetector configured to detect a plurality of target points in the angleof view, wherein each target point is detected based on receiving atleast a portion of photon energy of a light pulse in the series of lightpulses that is reflected back from one or more objects in the angle ofview.

FIG. 1 shows a schematic diagram 100 of an exemplary LIDAR sensingsystem, in accordance with various embodiments of the present invention.As shown in FIG. 1, a sensor system 110 can be used for detecting thedistance between the sensor system 110 and an object 104 within an angleof view of the sensor system 100. For example, the sensor system 110 canbe a LIDAR sensor system, which can detect the distance of the object104 based on measuring the time for light to travel between the sensorsystem 110 and the object 104, i.e. the a time-of-flight (TOF).

In accordance with various embodiments, different schemes can be usedfor implementing the LIDAR sensor system. For example, the LIDAR sensorsystem can be based on a monostatic (i.e. co-axial or in-line) scheme,in which case the outgoing beam 111 and the return beam 112 may share atleast a portion of the optical path. Alternatively, a LIDAR sensorsystem can be based on a different scheme such as a biostatic (i.e.bi-axial) scheme, in which case the outgoing beam 111 and the returnbeam 112 may be configured to travel along different optical paths.

As shown in FIG. 1, the sensor system 110 can include a light source101, which can generate a laser beam. For example, the laser beam can bea single laser pulse or a series of laser pulses. Furthermore, thegenerated laser beam can be collimated. As known by skilled person inthe art, collimated light refers to the light with parallel rays thatmay not spread substantially as the light propagates.

In accordance with various embodiments, a collimator can be used forcollimating the light generated by a point source. For example, a lens102 can be used for collimating the light generated by the light source101. Alternatively, mirrors such as spherical mirrors and/or parabolicmirrors can be used for collimating the light generated by a pointsource. For example, instead of using the lens 102, a mirror (not shown)may be placed behind the light source 101 to reflect the light raystoward the emitting direction in a substantially parallel manner.

As shown in FIG. 1, the collimated light can be directed toward a beamsteering/scanning device 103, which can induce deviation of the incidentlight. In accordance with various embodiments, the beamsteering/scanning device 103 can steer the laser light to scan theenvironment surrounding the sensor system 110. For example, the beamsteering device 103 can comprises various optical elements such asprisms, mirrors, gratings, optical phased array (e.g. liquid crystalcontrolled grating), or any combination thereof. Also, each of thesedifferent optical elements can rotate about an axis 109 that issubstantially common (hereafter referred as a common axis without unduelimitation), in order to steer the light toward different directions.I.e., the angle between rotation axes for different optical elements canbe the same or slightly different. For example, the angle betweenrotation axes for different optical elements can be within a range of0.01 degree, 0.1 degree, 1 degree, 2 degree, 5 degree or more.

Using the monostatic scheme as shown in FIG. 1, once the outgoing beam111 hits an object 104, the back-reflected portion of the light returnsin the exact opposite direction toward the LIDAR sensor system 110 andcan be collected eventually by a receiving device of the detector 105.Thus, using the monostatic scheme, the LIDAR sensor system 100 has theadvantage that the transmitting (or outgoing) field of view (FOV) (orangle of view) always aligns with the receiving FOV (or angle of view).Thus, the LIDAR sensor system 110 can have almost no blind area even atclose distances from LIDAR the sensor system 110.

In accordance with various embodiments, different mechanisms may be usedfor implementing the monostatic system. For example, a beam splitter 108can be arranged between the light source 101 (along with the lens 102)and the beam steering/scanning device 103. Alternatively, a LIDAR sensorsystem can be configured using a different co-aligned approach as shownin FIG. 6.

As shown in FIG. 1, the collimated light can pass through the beamsplitter 108 and impinge on the beam steering/scanning device 103.Subsequently, the beam steering/scanning device 103 can be controlled tosteer the light toward different directions, such as directions 111 and111′. Furthermore, the beam splitter 108 can be configured to redirectreturn beam arriving at the beam splitter 108 toward the detector 105.For example, the beam splitter 108 can comprise a mirror with anopening. The opening of the beam splitter 108 may allow the collimatedlight from the light source 101 to pass through (toward the beamsteering/scanning device 103), while the mirror portion of the beamsplitter 108 can reflect the return beam 112 toward a receiving lens106, which can collect and focus the returned beam on the detector 105.

In accordance with various embodiments of the present invention, thedetector 105 can receive the returned light and convert the light intoelectrical signals. For example, the detector 105 can take advantage ofa receiving device, such as an avalanche photodiode (APD), which is ahighly sensitive semiconductor electronic device. The APD can convertlight to electricity by exploiting the photocurrent effect.

In accordance with various embodiments of the present invention, ameasuring circuitry, such as a time-of-flight (TOF) unit 107, can beused for measuring the TOF in order to detect the distance to the object104. For example, the TOF unit 107 can compute the distance from TOFbased on the formula t=2D/c, where D is the distance between the sensorsystem and the object, c is the speed of light, and t is the time thattakes for light to take the round trip from the sensor system to theobject and back to the sensor system. Thus, the sensor system 110 canmeasure the distance to the object 104 based on the time differencebetween the generating of the light pulse 111 by the light source 101and the receiving of the return beam 112 by the detector 105.

In various embodiments, the light emission may be generated by the laserdiode at the nanosecond (ns) level. For example, the light source 101may generate a laser pulse with a duration close to 10 ns, and thedetector 105 can detect the return signal for a similar duration.Furthermore, the reception process can determine the pulse receivingtime, e.g. by detecting the rising edge of a measured electrical pulse.Here, the detection may take advantage of a multi-stage amplificationprocess. Thus, the sensor system 110 can use the pulse receiving timeinformation and the pulse emission information for calculating thetime-of-flight information in order to determine the distance.

FIG. 2 shows a schematic diagram of an exemplary LIDAR sensor systemusing a Risley prism pair, in accordance with various embodiments of thepresent invention. As shown in FIG. 2, the LIDAR sensor system 200 canuse a Risley prism pair, which may comprise two prisms 211-212, forlight steering/scanning (i.e. functioning as the beam scanning/steeringdevice 103 in the scheme as shown in FIG. 1). For example, the twoprisms 211-212 may be placed next to each other in a parallel fashion.In various embodiments, the prisms 211-212 may have a round crosssection and the central axes for the prisms 211-212 may coincide witheach other or with small angle. In various embodiments, the motor(and/or other power/control units) can cause the prisms 211-212 torotate about the common axis 209 (e.g. the central axis). I.e., theangle between rotation axes for different optical elements can be thesame or slightly different. For example, the angle between rotation axesfor different optical elements can be within a range of 0.01 degree, 0.1degree, 1 degree, 2 degree, 5 degree or more.

In various embodiment, the rotation frequency, geometry and orientationof the two prisms may be different, so that the relative angle betweenthe two prisms can change with time. Thus, when the laser beam passesthrough the prism pair 211-212, the direction of the outgoing beam maychange accordingly.

Using the monostatic scheme, once the outgoing beam 111 hits an object104, the back-reflected portion of the light returns in the oppositedirection toward the LIDAR sensor system 110 and can be collectedeventually by the receiving device of the detector 105. Due to timescale difference (i.e. the light speed is much faster than the rotationspeed of the prism), the angle change caused by the rotation of theprism during the measuring time (or TOF) may be negligible. Also, usingthe monostatic scheme, the LIDAR sensor system 100 has the advantagethat the transmitting FOV always aligns with the receiving FOV. Thus,the LIDAR sensor system 100 can have almost no blind area even at closedistances.

In accordance with various embodiments of the present invention, thedetector 105 can receive the returned light and convert the light intoelectrical signals. Also, a measuring circuitry, such as atime-of-flight (TOF) unit 107, can be used for measuring the TOF inorder for detecting the distance to the object 104. Thus, the sensorsystem 110 can measure the distance to the object 104 based on the timedifference between the generating of the light pulse 111 by the lightsource 101 and the receiving of the return beam 112 by the detector 105.

In accordance with various embodiments of the present invention, acontroller 208 can be used for controlling the steering of the laserbeam. For example, the controller 208 can control the respectiverotation (e.g. angular position and/or speed) of each prism 211 or 212,independently, about a rotation axis 209. In some cases, each prism canbe controlled by a separate controller. Additionally, the LIDAR sensorsystem 200 can obtain the angular position of each prism 211 or 212 inreal-time, in order to calculate the exact direction of the outgoingbeam. Such process can be repeated during the rotation of the prisms 211and 212, and information about the angle of view of the LIDAR sensorsystem 200 can be obtained.

FIG. 3 shows an exemplary refraction model 300 for using a Risley prismpair, in accordance with various embodiments of the present invention.

As shown in FIG. 3(a), a light ray 301 (with a unit vector {right arrowover (l)}) may transmit through a first medium with a refraction indexn₂ into a second medium a refraction index n₁. According to the Snell'slaw, the unit vector {right arrow over (v)} that represents the lightray 302 after refraction can be represented as{right arrow over (v)}=r{right arrow over (l)}+(rc−√{square root over(1−r ²(1−c ²))}){right arrow over (n)}where, r=n₁/n₂, c=−{right arrow over (n)}·{right arrow over (l)}, with{right arrow over (n)} representing the unit vector for the normaldirection 310 of the plane that separates the two mediums.

Thus, due to the difference in refraction index (i.e., the prisms canhave a refractive index that is different from the air), refraction mayoccur at the various air-substrate interfaces as the beam pass throughthe prism.

In the example as shown in FIG. 3(b), the beam {right arrow over (l₁)}may be incident upon the first prism at the first surface from the airat a vertical angle. Since the beam {right arrow over (l₁)} isperpendicular to the first surface, no refraction may occur (i.e. thebeam {right arrow over (l₂)} transmitting in the first prism is the sameas the incident beam {right arrow over (l₁)}). (In other examples,refraction may occur at the first surface if the incident angle is notnormal)

Furthermore, as the beam {right arrow over (l₂)} exits from the firstprism, refraction may occur at the second surface, since the beam {rightarrow over (l₂)} and surface normal direction {right arrow over (n₂)}has a non-vertical angle. Assuming that the refractive index of thefirst prism is n, then the unit vector {right arrow over (n₂)} for therefracted beam can be determined as in the following.{right arrow over (v ₂)}=r{right arrow over (l)}+(rc−√{square root over(1−r ²(1−c ²))}){right arrow over (n)}=n·{right arrow over (l₂)}+(−n·{right arrow over (l ₂)}·{right arrow over (n ₂)}−√{square rootover (1−n ²(1−(n·{right arrow over (l ₂)}·{right arrow over (n₂)})²))}){right arrow over (n ₂)}

Furthermore, when the beam {right arrow over (v₂)} incidents into thesecond prism, refraction occurs at the third surface (with a surfacenormal vector {right arrow over (n₃)}). The refracted beam {right arrowover (v₃)} can be calculated based on the refraction law, assuming thatthe two prisms have the same refractive index n.

$\overset{arrow}{v_{3}} = {{\frac{1}{n} \cdot \overset{arrow}{v_{2}}} + {( {{- \frac{\overset{arrow}{v_{2}} \cdot \overset{arrow}{n_{3}}}{n}} - \sqrt{1 - {\frac{1^{2}}{n}( {1 - ( \frac{\overset{arrow}{v_{2}} \cdot \overset{arrow}{n_{3}}}{n} )^{2}} )}}} )\overset{arrow}{n_{3}}}}$

Then, as the beam {right arrow over (v₃)} passing through the forthsurface (with a surface normal vector {right arrow over (n₄)}), theoutgoing beam can be calculated as in the following.{right arrow over (v ₄)}=n·{right arrow over (v ₃)}+(−n·{right arrowover (v ₃)}·{right arrow over (n ₄)}−√{square root over (1−n²(1−(n·{right arrow over (v ₃)}·{right arrow over (n ₄)})²))}){rightarrow over (n ₄)}

Thus, the final pointing direction of the refracted light 311′ can havea deviation angle from the original incident direction 311. Here, thedeviation angle θ between the outgoing beam {right arrow over (v₄)} andthe incident beam {right arrow over (l₁)} can be calculated using thefollowing formula.

$\theta = {\arccos( \frac{\overset{arrow}{l_{1}} \cdot \overset{arrow}{v_{4}}}{{\overset{arrow}{l_{1}}}{\overset{arrow}{v_{4}}}} )}$

As indicated in the above formula, the value of the angle θ can bedetermined based on the normal vectors {right arrow over (n₁)}, {rightarrow over (n₂)}, {right arrow over (n₃)} and {right arrow over (n₄)}for the four prism surfaces. Further as shown in FIG. 3(c), as theprisms rotate, the outgoing angle 311″ changes accordingly.

Referring back to FIG. 1, when the outgoing beam 111 hits the object104, the reflected or scattered light may spread over a large angle 120and only a fraction of the energy may be reflected back toward thesensor system 110. For example, the back-reflection can be describedusing the Lambertian scattering model (or other similar diffusivemodel), and the reflected energy (I) received by the detector 105 may beproportional to the square of the diameter (d) of the receiver andinversely proportional to the square of distance (D), i.e.I˜(d/D){circumflex over ( )}2. Thus, the intensity for the receivedlight for long distance ranging can be very small.

Furthermore, in order to boost the received signal level for detectingfar-away objects, a larger optical aperture is desirable, since themeasurement signal is proportional to the square of the diameter, d, ofthe receiver. Thus, it is preferable that the system form factor can beminimized while maintaining a relatively large optical aperture size.

In accordance with various embodiments of the present invention, variousmechanisms can be used to drive the rotation of the prisms. For example,hollow-core motors can be used for actuating the rotation of each prism.Thus, the sensor system can maximize the prism size for collecting theback-reflected light signal, and achieve high scanning speed due to theminimum load from these prisms. Alternatively, transmission through gearor belt can be used for actuating the rotation of each prism, which mayachieve similar effects.

FIG. 4 shows an exemplary illustration of rotating prisms in a LIDARsensor system 400, in accordance with various embodiments of the presentinvention. As shown in FIG. 4(a), a Risley prism pair can comprisemultiple prisms 411 and 412, each of which is embedded in a hollow-coremotor 413 or 414 respectively.

In accordance with various embodiments of the present invention, each ofthe hollow-core motors can be either an internal rotor motor or anexternal rotor motor. For example, both the hollow-core motors 413 and414 can be internal rotor motors or external rotor motors.Alternatively, the hollow-core motors 413 and 414 may be in differenttypes, i.e. one internal rotor motor and one external rotor motor.

In the example as shown in FIG. 4(a), both the hollow-core motors 413and 414 can be internal rotor motors. Each of the hollow-core motor 413or 414 can comprise a stator that is arranged outside a rotor viabearing support. For example, the prism 411 can be embedded in thehollow-core motor 413 and the prism 412 can be embedded in thehollow-core motor 414. Thus, the hollow-core motor 413 can actuate theprism 411 to rotate about a common axis 209 and the hollow-core motor414 can actuate the prism 412 to rotate about the common axis 209,independently.

Additionally, due to the wedge (or angled) shape of the prisms 411 and412, the rotating of each prism may be unstable since the massdistribution with respect to the rotation axis is imbalanced. As shownin FIG. 4, a small mass 415 and 416 may be added on (e.g. the outsideclamp ring of) the prisms 411 and 412 respectively, in order to balancethe mass distribution with respect to the rotation axis. Thus, the LIDARsensor system can improve stability for the rotating prisms and also canreduce noise and increase the lifetime for the rotating prisms.

In accordance with various embodiments of the present invention, variousmechanisms can be used for acquiring the precise angle (or angularposition) of each prism. The angle (or angular position) of each prismcan be defined in a rotational plane of each prism, which can be a planeperpendicular to the common rotational axis 209. For example, Hallsensors, optical encoders, and other similar sensors can be used by theLIDAR sensor system for precisely measuring the angle (or angularposition) of each prism in order for achieving high pointing accuracy.

As shown in FIG. 4(b), the deviation angle for the outgoing beam 401 andalso the return beam 402 can be effected by both the refractive indexand the inclined angle of the prisms. Thus, assuming the refractiveindex of the material is the same, the larger this inclined angle is thelarger the scanning angle (or FOV) can be.

On the other hand, materials with large refractive index can be used formaking the prism in order to achieve a large angle of view for the LIDARsensor system. For example, polycarbonate, a plastic material with arefractive index (n=1.567 @ 900 nm), can be used. Alternatively, glasseswith higher refractive index (n˜1.8) can be used. For example, using theexample of a Risley prism pair with two identical rotating prisms, theFOV for such a LIDAR sensor system may be approximately ±20° (or ±30°),when each rotating prism has an inclined angle of 17 degree (or 23degree). Additionally, other materials, such as liquid-filled prisms,which may have even higher refractive index, can be used. Alternatively,various diffracting or reflecting optical devices (such as transmissiongratings, reflection gratings, and mirrors etc.) may be used to replacethe prisms, as long as such device can divert the beam in a similarfashion.

FIG. 5 shows the configuration of an exemplary LIDAR sensor system usinga beam splitter, in accordance with various embodiments of the presentinvention. As shown in FIG. 5, the LIDAR sensor system 500 can takeadvantage of a Risley prism pair, which includes a pair of prisms 511and 512. Furthermore, each of the prisms 511 and 512 can be embedded ina hollow motor 513 and 514, respectively, and each prism can rotateindependently about a common axis (not shown).

Using the monostatic scheme, the transmitting optics and receivingoptics can be aligned along the same optical path. For example, a lightsource 501 can generate a laser beam that can be collimated.Additionally, a beam splitter 503 can be configured to allow thecollimated light to pass through toward the pair of prisms 511 and 512for light steering. Also, the beam splitter 503 can be configured toredirect the return beam toward a receiving unit 502, which may includea detector and one or more lens for collecting the returning light.Thus, the monostatic configuration can provide large optical aperturefor a LIDAR sensor system with limited form factor (or size). Also,using the monostatic configuration, a LIDAR sensor system can collectsufficient light signal to ensure a good signal to noise ratio, which isimportant for small form factor LIDAR sensor systems.

In accordance with various embodiments of the present invention, theRisley prisms enjoy various advantages, such as compactness, relativeinsensitivity to vibration, high scanning speed and low moment ofinertia. Also, each individual prism in the Risley prism pair can beconfigured with an independent rotational axis. As shown in FIG. 5, theLIDAR sensor system has a dimension (or form factor) of length (L),width (W), and height (H). Furthermore, the optical aperture area, whichcan be estimated as a circle with a diameter d, occupy a large portionof the cross section (L×W). Thus, the LIDAR sensor system can have alarge form factor efficiency, which can be defined as a ratio of theoptical aperture size over the LIDAR system form factor.

FIG. 6 shows an alternative exemplary LIDAR sensing scheme 600, inaccordance with various embodiments of the present invention. As shownin FIG. 6, a sensor system 610 can be used for detecting the distancebetween the sensor system 610 and an object 604 within an angle of viewof the sensor system 610. For example, the sensor system 610 can be aLIDAR sensor system, which can detect the distance between the sensorsystem 610 and the object 604 based on measuring the time for light totravel between the sensor system 610 and the object 604, i.e.time-of-flight (TOF).

In accordance with various embodiments, the LIDAR sensor system can bebased on a monostatic scheme, in which case the outgoing beam 611 andthe return beam 612 can share at least a portion of the optical path(i.e. in a co-axial or in-line system).

As shown in FIG. 6, the sensor system 610 can include a light source601, which can generate a laser beam, such as a single laser pulse, or aseries of laser pulses. Additionally, the generated laser beam canoptionally be collimated (e.g. using a lens 602). The light source 601(including the collimating lens 602) can be arranged between thedetector 605 and the beam steering/scanning device 603.

As shown in FIG. 6, the collimated light can be directed toward the beamsteering/scanning device 603. Subsequently, the beam steering/scanningdevice 603 can steer the light to different directions, e.g. thedirections 611 and 611′.

In accordance with various embodiments, various types of opticalelements can be used for steering the laser light for scanning theenvironment surrounding the sensor system. For example, the beamsteering/scanning device 603 can comprises various optical elements suchas prisms, mirrors, grating, optical phased array, or any combinationthereof. Also, each of these different optical elements can rotate aboutan axis that is substantially common (hereafter referred as a commonaxis without undue limitation), in order to steer the light towarddifferent directions. I.e., the angle between rotation axes fordifferent optical elements can be the same or slightly different. Forexample, the angle between rotation axes for different optical elementscan be within a range of 0.01 degree, 0.1 degree, 1 degree, 2 degree, 5degree or more.

In one example, the beam steering/scanning device 603 can be a Risleyprism pair, which comprise two prisms (each with a refractive index thatis different from the air). The beam may be refracted at differentair-substrate interface. As the pair of prisms rotating about a commonaxis (not shown), the angle of deviation between the final pointingdirection 611 or 611′ and the original incident direction may bechanging. Such changing deviation can be used for scanning theenvironment surrounding the sensor system by rotating the prisms.

As shown in FIG. 6, using a monostatic scheme, once the outgoing beam611 hits an object 604, the return beam, i.e. the back-reflected portionof the light, returns in opposite direction towards the sensor system610 and can be collected by the detector 605. Additionally, a receivinglens 606 can be used for collecting the returned light and focusing thereturned light to the detector 605. Since the detector 605 is arrangedfacing the beam steering/scanning device 603, from which direction thelight returns, there is no need for additional optical devices such as abeam splitter as shown in FIG. 1.

In accordance with various embodiments, different configurations can beused for arranging the receiving lens 606, which can collect thereturned beam and focus the returned beam toward the detector 605. Forexample, the receiving lens 606 can be arranged between the light source601 and the detector 605 as shown in FIG. 6. Alternatively, thereceiving lens 606 may be arranged alongside or in front of the lens602.

Alternatively, instead of arranging the light source directly in theaperture, an emitting structure with a mirror can be positioned betweenthe detector 605 and the beam steering/scanning device 603. Furthermore,the sensor system 610 can optimize the size of the light source or theemitting structure, in order to block less return beam.

In accordance with various embodiments of the present invention, thedetector 605 can receive the returned light and convert the light intoelectrical signals. For example, the detector 605 can take advantage ofa receiving device, such as an avalanche photodiode (APD). The APD is ahighly sensitive semiconductor electronic device that can convert lightinto electrical signals by exploiting the photocurrent effect.

In accordance with various embodiments of the present invention, ameasuring circuitry, such as a time-of-flight (TOF) unit 607, can beused for measuring the distance to the object 604. For example, the TOFunit 607 can compute the TOF based on the time for light to travelbetween the sensor system and the object. Thus, the sensor system canmeasure the distance of the object 604.

FIG. 7 shows an exemplary illustration of an alternative LIDAR sensorsystem, in accordance with various embodiments of the present invention.As shown in FIG. 7(a), the LIDAR sensor system 700 can take advantage ofa pair of prisms 711 and 712 (e.g. a Risley prism pair), each of whichcan be embedded in a hollow motor 713 or 714 respectively. Furthermore,each prism 711 or 712 can rotate independently about a common axis (notshown).

In accordance with various embodiments of the present invention, theRisley prisms enjoy various advantages, such as compactness, relativeinsensitivity to vibration, and low moment of inertia. Also, eachindividual prism in the Risley prism pair can be configured with anindependent rotational axis.

Using the monostatic scheme, the transmitting optics and receivingoptics can be aligned along the same optical path. For example, anemission structure 720 can be arranged between the receiving lens 705and the prism 712. The emitting structure 720 can include a mirror,which can be mounted or integrated on one end (e.g. the distal end) ofthe emitting structure 720. Furthermore, the sensor system 710 canoptimize the size of the emitting structure, in order to block lessreturn beam.

As shown in FIG. 7(a), a light source 701, which is arranged by a sideof the LIDAR sensor system (e.g. on another end, such as the proximalend, of the emitting structure 720), can generate a laser beam, which iscollimated. The mirror 702 can reflect the collimated light toward theprisms 711 and 712, which in turn steer the light toward the outgoingdirection. Then, the receiving lens 705 can collect the return beam anddirect it toward a detector 706.

In the example as shown in FIG. 7, the LIDAR sensor system has adimension (or form factor) of D and H, and the optical aperture area canbe estimated as a circle with a diameter d. The optical apertureoccupies a large portion of the system cross section. Thus, the LIDARsensor system can have a large form factor efficiency, which can berepresented as the optical aperture size/LIDAR system form factor.

As shown in FIG. 7, the LIDAR sensor system can use almost the entireprism area for collecting the back-reflected light signal. Since theprism area constitutes a large portion of the system form factor, theLIDAR sensor system's form factor can be minimized while maintaining alarge optical aperture. The LIDAR sensor system 700 can boost the signallevel for detecting far-away objects by taking advantage of a largeoptical aperture. Thus, a light weight, small form factor LIDAR sensorsystem can be achieved. Using such a monostatic configuration, the LIDARsensor system with a small form factor can achieve large usable opticalaperture and can collect sufficient light signal to ensure a good signalto noise ratio, which is important for detecting objects in thesurrounding environment.

FIG. 8 shows an exemplary illustration of a LIDAR sensor system withdifferent light emitting configurations, in accordance with variousembodiments of the present invention. As shown in FIG. 8(a), a mirror801, which is either mounted on or integrated as part of the emittingstructure 720, can reflect the light generated by the light sourcetoward the emitting direction. Since the emitting structure 720 ispositioned within the aperture, the emitting structure 720 may block aportion of the aperture area, which could otherwise be used forreceiving the return beam.

As shown in FIG. 8(a), the mirror 801 can be positioned at the center ofthe aperture. Correspondently, the emitting structure 720 may beextended to the center of the aperture, which may block a substantialarea in the optical aperture. On the other hand, as shown in FIG. 8(b),the mirror 802 can be positioned off-centered to the extent that thereflected light does not hit anything in the outgoing direction. Thus,less aperture area may be blocked by the emitting structure 721.

FIG. 9 shows an exemplary illustration of optimizing a light emittingstructure in a LIDAR sensor system, in accordance with variousembodiments of the present invention. As shown in FIG. 9(a), due to theinternal structure of the laser diode, the laser beam profile 901 mayhave a rectangular or elliptical shape (i.e. with a long axis 902 and ashort axis 903).

In accordance with various embodiments of the present invention, theemitting structure 904 can be configured in a geometry that can takeadvantage of the laser beam profile 901 in order to block less light forthe receiving system.

As shown in FIG. 9(b), the emitting structure 904 can be configured in arectangular block shape. The rectangular shaped surface of the emittingstructure 904 facing toward the return beam 912 can be configured tohave a width that matches the short axis 903 of the laser beam profile901. Also, the emitting structure 904 can be configured to have adimension that matches the long axis 902 of the laser beam profile 901.Thus, the mirror 905 on the emitting structure 904 can reflect the fullprofile of the laser beam toward the emitting direction 911.

As shown in FIG. 9(b), a light source (not shown) can generate a laserbeam 910 with the beam profile 901 that is collimated. The collimatedlight 910 can propagate through the emitting structure 904 before beingreflected toward the emitting direction (i.e. the outgoing beam 911) bya mirror 905. Subsequently, the return beam 912 can share at least aportion of the optical path with the outgoing beam 911 and eventually becollected by the receiving unit 920 (which may include a lens and adetector). Since cross section of the emitting structure closely matchesthe outgoing laser beam profile, the emitting structure maximizesoutgoing beam while minimizing unnecessary blockage of the return beam.

In accordance with various embodiments of the present invention, usingthe monostatic scheme, the LIDAR sensor system can have the advantagethat it is easier to align the light source and the receiver without ablind area. Also, the monostatic system can minimize the overall systemform factor while optimizing the optical aperture for excellent signalto noise ratio. The monostatic system can have a large field-of-view(FOV), can achieve high scanning speed and good resolution for a singlepair of laser emitter and detector. Thus, the monostatic system can havegood performance while enjoying low cost and small size. Additionally,the monostatic system allows for dynamically adjustable pointingcapability and supports different scanning patterns.

In accordance with various embodiments of the present invention,different approaches can be used separately or collectively forpreventing optical contamination (such as undesired back-reflection)caused by various types of stray light.

FIG. 10 shows a schematic diagram of preventing optical contamination inan exemplary LIDAR sensor system, in accordance with various embodimentsof the present invention. As shown in FIG. 10, the LIDAR sensor system1000 can reject various types of stray light.

The optical contamination may be caused by various types of stray light,such as the reflected light and/or scattered light. In the examples asshown in FIG. 5 and FIG. 7, the LIDAR transmission light may contaminate(or interfere) with the receiving of return beam by the detector. Suchcontamination (or interference) may cause trouble in recognizing theclose distance echoes (i.e. the T=0 problem). Also, due to thescattering and reflecting of the emitted light signal on the propagationpath (such as the glass cover, optical element, and sidewalls along theoptical path), a portion of the transmitted laser light may be collectedby the detector 1005.

The light intensity for the optical contamination (or interference) canbe considerably high, which may lead to the circuit system saturation(e.g. in the high magnification scenarios). The optical contamination(or interference) may result in an amplifier failure for a period oftime (e.g. ˜100 ns for the range of 15 m). As a result, a LIDAR sensorsystem may not be able to detect objects in the surrounding environmentin close proximity. Additionally, the optical contamination (orinterference) may cause difficulty in recognizing the rising edge of theelectrical signal for received light, which can be troublesome indetermining the light pulse receiving time (˜10 ns). Additionally, theoptical contamination may cause false signals at random time, which mayprevent detection of the true optical signal and thus the TOF. Also,there may be electrical signal interference (since electromagnetic waveis prone to interfere due to the close proximity between the lightsource emitting opening and the detector).

In accordance with various embodiments of the present invention, variousapproaches can be used for rejecting scattered and reflected light in aLIDAR sensor system, in order to solve the T=0 problem.

For example, various optical elements in the LIDAR sensor system,through which the laser light is transmitted along the optical path, maybe slightly tilted to avoid direct reflection. As shown in FIG. 10, theprism 1011 can be configured with an angle 1021, and the prism 1012 canbe configured with an angle 1022. Thus, as the prisms 1007 and 1008rotate, e.g. about a common axis 1009, a portion of the light pulses1010 that is reflected back from the various reflective surfaces, e.g.the beam 1016, 1018 and 1023, can avoid hitting the detector 1005. Invarious embodiments, the different prisms 1011 and 1012 can beconfigured with the same tilt angle. Alternatively, the different prisms1011 and 1012 may be configured with different tilt angles to achievesimilar or better outcome.

Also, the enclosing window 1013 can be configure with an angle 1023, sothat the direct reflection light 1018 can be direct to avoid thedetector.

Furthermore, anti-reflection coatings can be applied to the surfaces ofvarious optical elements in the LIDAR sensor system to reduce the directreflection and scattered light. As shown in FIG. 10, various surfaces ofthe prisms 1011 and 1012 can be applied with coating 1008. Also, thecoating 1008 may be applied on the two surfaces of the emission window1013 of the enclosed housing 1015.

Additionally, in order to further reduce the contamination (orinterference), a band-pass filter centered at the laser wavelength canbe used to reject out-of-band lights. As shown in FIG. 11, multiplelayers of coatings can be applied to create a band-pass filter 1100 withnarrow passing band. In the example as shown in FIG. 11(a), a firstlayer of coating 1101 may only allow light with relative long wavelengthto pass and a second layer of coating 1102 may only allow light withrelative short wavelength to pass. Collectively, a band-pass filter withnarrow passing band 1110 can be achieved. Alternatively, in the exampleas shown in FIG. 11(b), a first layer of coating 1111 may allow lightwith relative wide band of wavelength to pass and a second layer ofcoating 1112 may allow light in multiple narrow bands of wavelengths topass. Collectively, a band-pass filter with narrow passing band 1110 canbe achieved. Also an optional layer 1120 can be applied to furthermodify the narrow passing band 1110.

Furthermore, other optical devices, such as an etalon or Fabry Perotinterferometer (FPI), can be applied on the surfaces of the prisms 1011and 1012 (e.g. along with various types of coatings). For example, theFPI can be either a standalone FPI or a stationary FPI. The standaloneFPI can be electrically controlled so that the peak wavelength can varyaccordingly, which is beneficial for tracking the change of laserwavelength and continuously block all other interferences. On the otherhand, the stationary FPI can take advantage of a thin film coated on asurface. The thin film can comprise two high reflective coatingsseparated by a spacer.

Referring back to FIG. 10, different approaches can be used for reducingthe scattered light. For example, oxidation or dark paint 1007 can beapplied on the inner surfaces of the supporting structures or sidewallsof the optical components to reduce the scattered stray light.

In accordance with various embodiments of the present invention,specific optical structures or devices can be used to further reject thestray light. As shown in FIG. 10, the LIDAR sensor system 1000 can use abaffle tube 1006, such as a blackened thin laser beam tube, to extendthe laser exit opening on the beam splitter 1003 (e.g. the opening on amirror). The baffle tube 1006 can extend the laser exit opening tosignificantly reduce the stray light, which may potentially interferewith the receiving of return beam at the detector 1005.

Thus, the LIDAR sensor system 1000 can separate the actual echoes fromthe scattered or back-reflected transmitting beam and solve the T=0problem.

Additionally, other types of contaminations (or interferences), such asthe sunlight, may be presented in the LIDAR sensor system 1000. Thedirect sunlight or scattered sunlight may go into the receiver of thedetector 1005, and cause receiver saturation or trigger false signals.For example, the sun shining on the wall or other surfaces behind atarget object, may be reflected toward the LIDAR sensor system. Thereflected sunlight may be more intensive than the laser light that isreflected back from the object, which may cause measurement errors.

In accordance with various embodiments of the present invention, variousapproaches can be used separately or collectively for preventing thecontamination (or interference) by the sunlight. For example, opticalisolation (e.g. a housing 1015 that encloses the various opticalcomponents and the detector 1005) can be used for reducing thecontamination (or interference) caused by the sunlight. Additionally,the LIDAR sensor system can use an optical filter, which allows only thelight with a specific wavelength range (e.g. laser wavelength+/−10 nm)to pass through (e.g. as shown in FIG. 11). Thus, the optical filterallows the return beam to pass through while reducing the effect ofsunlight.

Another approach is to increase the laser power. Also, the LIDAR sensorsystem can use a very small instantaneous field of view (IFOV) or usepulsed light output, which can increase instantaneous power such thatthe intensity of the return beam can be comparable to or stronger thanthat of the sunlight.

In accordance with various embodiments of the present invention, thereceiving device for the detector 1005 can be configured with a profilethat matches the laser beam profile (i.e. the emitting and receivingIFOV) for rejecting the stray light. For example, the profile for thedetector 1005 can be determined based on the laser beam profile (andcorresponding optical configuration), e.g. using a formula, I/f1=L/f2,where I indicates the dimension of the receiving device, L indicates theprofile of the laser beam, f1 is the focal length of the lens 1004 andf2 is the focal length of the lens 1002. Thus, light signals other thanthe return beam can be rejected.

In accordance with various embodiments of the present invention, varioustypes of optical devices, such as a spatial filtering device and/or afield stop aperture device, can be arranged along the optical path ofthe return beam to reject various stray lights. For example, the spatialfiltering and the field stop aperture can be used to reject scatteredsunlight. Also, the LIDAR sensor system can employ a circuit that candynamic adjust APD gain with sunlight detection.

FIG. 12 shows a schematic diagram of spatial filtering in an exemplaryLIDAR system, in accordance with various embodiments of the presentinvention. As shown in FIG. 12(a), the spatial filtering device 1210 canbe arranged between the receiving lens 106 and the detector 105. Thespatial filtering device 1210 can comprise a screen 1210 with an opening1220. In order to reject stray light, the opening 1220 may be arrangedat the focal point of the receiving lens 106. Thus, only the returnbeam, which is reflected back from an object in the angle of view of theLIDAR sensor system that travels at the “right” direction toward thereceiving lens 106, can pass through this opening, while the scatteredlight in other random direction can be blocked. Similarly, scatteredsunlight may also be blocked.

As shown in FIG. 12(b), the opening on the spatial filtering device 1210can be either a small pinhole 1221 (e.g. in round shape) or a slit 1222(e.g. in rectangular shape). For example, the shape of the opening 1220on the spatial filtering device 1210 can be configured to match thelaser beam profile. In accordance with various embodiments, due to theinternal structure of most semiconductor laser emitter (or diode), thelaser beam profile can be in a rectangular or elliptical shape. In thecase of the pinhole, the round shape 1221 does not match the laser beamprofile well. Thus, more stray light may pass through the opening andreaches the receiving device. On the other hand, when a rectangularshape slit is used, the amount of stray light passing through theopening may be substantially reduced. Thus, in the example as shown inFIG. 12(b), it is preferable to configure the opening 1220 as arectangular slit 1222, or other suitable shape that matches the laserbeam profile.

FIG. 13 shows schematic diagrams of using alternative approaches forproviding spatial filtering in an exemplary LIDAR sensor system, inaccordance with various embodiments of the present invention.

As shown in FIG. 13(a), the spatial filtering device 1320 and anadditional lens 1322 can be arranged between the receiving lens 106 andthe detector 1305. The lens 1322 can be used for focusing the filteredlight, which passes through the spatial filtering device 1320, onto thereceiving device 1305 of the detector. Thus, the detector 1305 canafford to use a receiving device 1205 with a substantially smallerreceiving area.

Also as shown in FIG. 13(b), the spatial filtering device 1330 can bearranged between the receiving lens 106 and the prisms 211 and 212.Thus, the spatial filtering mechanism can be applied to blockundesirable light in both the outgoing beam and the return beam, therebyimproving efficiency.

FIG. 14 shows a schematic diagram of using a field stop aperture (FSA)in an exemplary LIDAR sensor system, in accordance with variousembodiments of the present invention. As shown in FIG. 14, a series offield stop apertures 1411-1413 can be placed in front of the detector105, and the stray light hitting these structures may be reflected back.Thus, the interference on the detector 105 can be reduced.

FIG. 15 shows an exemplary configuration of a LIDAR sensor system thatcan reduce undesired back-reflection, in accordance with variousembodiments of the present invention. As shown in FIG. 15, the LIDARsensor system 1500 can take advantage of a pair of prisms 1511 and 1512,each of which can be embedded in a hollow motor 1513 or 1514respectively. Furthermore, each prism can rotate independently about acommon axis 1507, which is tilted (with an angle) relative to theoptical axis 1506 to reduce direct reflection of the emitting light intothe receiving devices of the detector 1505.

Furthermore, a light source 1501 can generate a laser beam that can becollimated using one or more lens 1502. Additionally, a beam splitter1503 can be configured with a baffle tube 1515 to allow the collimatedlight to pass through and be directed toward the pair of prisms 1511 and1512 for light steering. On the other hand, the beam splitter 1503 canredirect the return beam toward a receiving unit, which may include adetector 1505 and one or more lens 1504 for collecting the returnedlight. Additionally, the various optical components can be enclosed in ahousing 1515 to ensure optical isolation, which can be beneficial forreducing optical contamination (or interference) for the detector 1505.

FIG. 16 shows a flowchart of sensing using a LIDAR sensor system, inaccordance with various embodiments of the present invention. As shownin FIG. 16, at step 1601, the LIDAR sensor system can generate a lightthat is collimated. At step 1602, the LIDAR sensor system can direct thelight toward a plurality of optical elements, each rotatable about acommon axis independently, wherein the plurality of optical elementsoperate to collectively direct the light pulse to one or more objects inan angle of view of the sensor system. At step 1603, the LIDAR sensorsystem can receive, via the plurality of optical elements, at least aportion of photon energy of the light that is reflected back from theone or more objects in the angle of view. Furthermore, at step 1604, theLIDAR sensor system can convert the received photon energy into at leastone electrical signal.

FIG. 17 shows an exemplary illustration of controlling a LIDAR sensorsystem, in accordance with various embodiments of the present invention.As shown in FIG. 17 (also as indicated in various exemplaryillustrations in the above), a LIDAR sensor system 1710 can comprise alight source 1701, a scanning device 1702, and a receiving device 1703.The light source 1701 can generate a laser beam, such as a single laserpulse, or a series of laser pulses, which can be collimated. Thescanning device 1702 can steer the collimated light for detectingobjects in the surrounding environment. Then, a portion of the lightthat is reflected back from one or more objects in an angle of view 1730in the surrounding environment can be directed to the receiving device1703 (e.g. a detector).

Furthermore, a controller, such as a LIDAR sensor system controller1720, can be used for controlling the operation of the LIDAR sensorsystem 1710. For example, a laser pulse trigger 1711 can be used forcontrolling the generation of the laser pulses, a scanner 1712 can beused for controlling the scanning device, and a measurement unit 1713can be used for processing the received signals and measuring thedistances to one or more objects 1721-1723 in the angle of view 1730.

In accordance with various embodiments, the laser pulse trigger 1711 canbe used for controlling the light source 1701 to generate a series oflight pulses for scanning the environment. The laser pulses can betriggered in different manners. For example, the laser pulse can betriggered at certain time intervals. For example, the time intervals canbe pre-configured or pre-determined. Alternatively, the light pulses canbe triggered dynamically in-flight (e.g. by first sensing the pointingdirection then determining whether to fire a pulse).

In accordance with various embodiments, a scanner 1712 can control thescanning device 1702 to steer the light pulses toward differentdirections in order to scan the surrounding environment of the LIDARsensor system 1710. For example, the scanning device 1702 can be aRisley prism pair, which comprise two prisms, each with a refractiveindex that is different from the air. The light pulses may be refractedat different air-substrate interfaces. Thus, the final pointingdirection for each light pulse can have a deviation from the originalincident angle. This deviation can be used for scanning the environmentsurrounding the sensor system as the two prisms rotate.

In accordance with various embodiments, the LIDAR sensor system 1710 canemploy a measurement unit 1713, such as a TOF unit for determining thedistance to one or more objects 1721-1723 in the angle of view 1730 bymeasuring the time taken by the laser light to travel between thedetected object and light source 1701/receiving device 1703.

In accordance with various embodiments, the LIDAR sensor system 1710 canacquire a point cloud 1731 based on scanning the surroundingenvironment. For example, each point in the point cloud can correspondto the transmitting of an outgoing signal (i.e. a light pulse) and thereceiving of a target signal that is reflected back from an object 1721,1722, or 1723 in the angle of view 1730.

In accordance with various embodiments, each target point in the pointcloud can be acquired within a coordinate system. For example, the LIDARsensor system can determine the angle of the outgoing signal at a timepoint based on instantaneous angular position of each said opticalelement. Furthermore, the LIDAR sensor system can determine the distanceassociated with the target point based on TOF between the transmittingof an outgoing signal and the receiving of a target signal. Thus, thecoordinates or spatial location of each target point in the coordinatesystem can be determined based on instantaneous angular position of eachsaid optical element and a distance associated with the target point.

In various embodiments, due to the potentially complex geometry,multiple target points may be detected for each object 1721, 1722, or1723. Thus, by acquiring a large number of target points in the pointcloud, the LIDAR sensor system 1710 can reveal detailed informationabout the surrounding environment.

In accordance with various embodiments, the LIDAR sensor system 1710 canbe configured to meet various constraints. For example, in order to meetthe constraint prescribed for eye safety, the LIDAR sensor system 1710may be configured to adjust the instantaneous laser pulse energyintensity and/or the laser repetition rate, for controlling a maximumamount of energy during a certain time period. Also, the LIDAR sensorsystem 1710 may generate laser pulses with different width or energylevel.

In accordance with various embodiments, the LIDAR sensor system 1710 cantrigger laser emission based on different strategies or scanning modes.For example, the LIDAR sensor system 1710 may operate in a raw scanmode, a fine scan mode, or a fixed point scan mode.

In the raw scan mode, the LIDAR sensor system 1710 can acquire a sparsepoint cloud, by firing laser pulses, which are more powerful but lessfrequently, to detect individual target points at long range and withhigh precision. Thus, the system can obtain a big picture about thesurrounding environment, e.g. by randomizing the scanning direction inspace correspondingly.

In the fine scan mode, the LIDAR sensor system 1710 can acquire moretarget points that can reveal more detailed information about the scene,by firing laser pulses more frequently (i.e. at a higher laser emissionrate). Here, each pulse can be configured to be less powerful to meetthe eye safety constraint.

Additionally, the LIDAR sensor system 1710 can perform fixed point scan,if a particular angle or direction in the surrounding environment is ofinterest. For example, a specific direction in the surroundingenvironment may become interesting, e.g., after detecting a personcrossing the street, after the raw scan and/or the fine scan. The LIDARsensor system can rotate the prisms to steer the laser pulses toward theparticular direction, and fires a series of laser pulses in (and around)that particular direction. In such cases, since the laser is steered forscanning a small area, relatively more laser pulses can be used fordetecting objects in the particular direction. Laser energy can be highenough to ensure both the accuracy and range of the measurement. Sincesmaller area is scanned, relatively more repetitions could be used toobtain the averaged signal with better noise figures. Thus, the LIDARsensor system 1710 can achieve a better signal to noise ratio than thegeneral scan, even though the laser repetition rate may be limited foreye safety.

FIG. 18 shows an exemplary illustration of a deviation model forrotating a Risley prism pair, in accordance with various embodiments ofthe present invention. As shown in FIG. 18(a), for a single prism,assuming the prism has a uniform refraction index, the refracted beamcan scan a complete circle 1810 once the prism rotates 360 degrees. Asthe prism rotates, the instantaneous deviation of the laser beam can berepresented using a point 1802 associated with a vector 1801, thedirection of which represents the angle of the deviated beam in therotating plane caused by the rotation of the prism, and the magnitude ofwhich represents the deviated angle.

Furthermore, two prisms can be arranged in a parallel fashion (orstacked) along the optical path. Thus, the final pointing direction ofthe deviated beam caused by the rotation of the two prisms can berepresented using a final point, which is obtained by adding the firstprism vector and a second prism vector together. According to Snell'sLaw, the second vector may vary slightly in length with respect to therelative angle, but the vector length may be treated as a constant usingthe paraxial approximation (which applies to small angles).

As shown in FIG. 18(b), the point 1813 on the outside circle 1820, whichrepresents the maximum deviation, can be reached when the two prisms areoriented the same way (i.e. the first prism vector 1811 and the secondprism vector 1812 are aligned toward the same direction). On the otherhand, the point 1823 represents a deviation that can be reached when thetwo prisms are not oriented the same way (i.e. the first prism vector1821 and the second prism vector 1822 are in the different directions).Thus, in the cases when the two prisms are identical, the LIDAR sensorsystem can reach any point within the outer circle 1820 using certainvector configuration (i.e. orienting the two prisms appropriately).

In accordance with various embodiments of the present invention, thesteered beam can travel about the rotation axis as the pair of prismsrotate. In the example as shown in FIG. 2, a controller 208 can be usedfor controlling the rotation of each individual prism. Each of theprisms rotates independently to collectively steer the beam to adirection that can be determined by the instantaneous position of theprism and the incident angle of the (incoming) beam. Thus, the steeredbeam can used for scanning the surrounding environment within an angleof view. Depending on the respective rotation of each individual prism,using the paraxial approximation, the mathematical expression for thefinal beam angle can be represented as{right arrow over (P)}={right arrow over (A)}+{right arrow over (B)}where {right arrow over (A)} and {right arrow over (B)} are the twovectors defined respectively by the two prisms.

Accordingly, in Cartesian coordinates, the final beam angle isA _(x) =A cos(ω_(A) t+φ _(A))A _(y) =A sin(ω_(A) t+φ _(A))B _(x) =B cos(ω_(B) t+φ _(B))B _(y) =B sin(ω_(B) t+φ _(B))where, A and B are the magnitudes (which can be the same for a pair ofidentical prisms), ω is the rotation angular speed and φ is the initialangle for each prism respectively.

In accordance with various embodiments, depending on the respectiverotation of each individual prism, such as the relative rotation speedbetween two prisms, the scanning may be performed in different patterns.FIG. 19 shows exemplary illustration of different scanning patternsusing a LIDAR sensor system, in accordance with various embodiments ofthe present invention. By controlling the rotation of the two prisms,the LIDAR sensor system can achieve different scanning patterns, whichmay be characterized as Lissajous figures.

As shown in FIG. 19(a), when the difference between the two angularspeeds is small (i.e. when the relative speed is small), a spiral shapescan pattern may be achieved (i.e., the light pulses are spread acrossthe angle of view, which is favorable for scanning). On the other hand,as shown in FIG. 19(b), when the difference is large (or when two prismsare rotating in different direction), a flower shape scan pattern can beachieved (i.e., the light pulses are denser toward the center of theangle of view, which is favorable for ranging).

In accordance with various embodiments, the LIDAR sensor system candynamically adjust the angular positions or speeds of the two prisms forvarious scanning needs. For example, the dynamic control approach can beused for achieving different point cloud patterns.

Using the example as shown in FIG. 3, when both prisms rotate atconstant angular velocity, the laser pulses may be denser toward thecenter. In some embodiments, the LIDAR sensor system can increase theangular velocity difference between the motors when the prisms are closeto the opposite directions (i.e. when that beam is close to the center),in order to uniformly distribute the laser pulses among the differentscanning areas.

In accordance with various embodiments, the emitting frequency may bedynamically adjusted in order to achieve a uniform scan of theenvironment. For example, in the case when the deviation angle for eachprism is constant and the rotation speed is constant, the emittingfrequency can be configured to be proportionally to sin(φ₁−φ₂), where φ₁and φ₂ are the respective instantaneous angles for each prism and φ₁−φ₂is the angle difference at any given time point. For example, whenφ₁−φ₂=0, the two prisms have the same orientation. On the other hand,when φ₁−φ₂=180°, the two prisms have the opposite orientations.

Thus, the LIDAR sensor system can achieve similar or uniform scanningspeed at different directions with the angle of view in order to obtaina uniformly scanned (or distributed) point cloud. FIG. 20 showsexemplary illustration of a uniform scanning pattern using a LIDARsensor system, in accordance with various embodiments of the presentinvention.

In accordance with various embodiments, the LIDAR system can dynamicallyadjust the angular position of each prism to steer the laser beam to aparticular region of interest (ROI). Using such method, the LIDAR systemcan achieve directional beam scanning by accurately controlling theangular positions of the two prisms, so that the LIDAR sensor system canprecisely point the laser beam to a particular direction to measure thedistance for an object at the angle. Also, the LIDAR system can achieveobject tracking by controlling the two prism angular positions, so thatthe LIDAR sensor system can track certain moving object (e.g. using afeedback control loop).

FIG. 21 shows an exemplary illustration of controlling beam steering fora LIDAR sensor system, in accordance with various embodiments of thepresent invention. As shown in FIG. 21, the point 2113 associated with adeviation vector {right arrow over (l)} 2101 represents an azimuthalangle α 2102 that is desired. Accordingly, the LIDAR sensor system 2100can rotate the two prisms to angular positions that can deviate the beamby {right arrow over (P₁)} 2111 and {right arrow over (P₂)} 2112respectively. Thus, the angle β 2103 can be obtained based on themagnitude of {right arrow over (l)} and the magnitudes of {right arrowover (P₁)} 2111 and {right arrow over (P₂)} 2112, and the angles (ororientations) for the two prisms can be determined as α+β and α−βrespectively.

As {right arrow over (l)} changes, i.e. when the desired pointingdirection is changed (in either magnitude or angle, or both), the LIDARsensor system can be reconfigured according to the calculated β in orderto adjust for the change. Also, the LIDAR sensor system may directlyvary the angle α to follow the azimuthal angle change. For example,assuming the prisms are identical and using paraxial approximation (i.e.{right arrow over (P₁)} 2111 and {right arrow over (P₂)} 2112 have thesame magnitude or P=|{right arrow over (P₁)}|=|{right arrow over(P₂)}|), the angle β 2103 can be calculated as β=arccos (|{right arrowover (l)}|/2P). Also, the angles for the two prisms can be swapped andthe final pointing vector {right arrow over (l)} 2101 would remain thesame.

In accordance with various embodiments, various approaches can be usedfor achieving a three dimensional scan. In various embodiments, the twoprisms may not be identical. For example, one prism can have a largerinclined angle than the other prism. Additionally, the prism can bereplaced with a transmission grating for the same or similar effect.Also, a rotating prism can be combined with other scanning methods.

FIG. 22 shows an exemplary illustration of alternative LIDAR sensorsystems, in accordance with various embodiments of the presentinvention. As shown in FIG. 22(a), the light generated by a light sourcecan first go through a prism, which can direct the light to a scanningmirror. Then, the scanning mirror can redirect the light to detect thesurrounding environment. Similarly, as shown in FIG. 22(b), the lightgenerated by a light source can first go through a scanning mirror thatoperates to reflect the light to a prism, which in turn can steer thelight to different directions.

For the above examples, the LIDAR system can steer the light to anoutgoing direction that is substantially different from the originalemitting direction, due to reflection. Also, in either example, both theprism and mirror may be rotatable. Thus, the sensor system can adjustand steer the lights toward different directions in the environment.

Additionally, as shown in FIG. 22(c), the LILDAR sensor system can takeadvantage of multiple prisms, each of which can be individuallycontrolled to rotate about a common axis independently. Thus, the LILDARsensor system can have more control in scanning the surroundingenvironment.

In accordance with various embodiments, the LIDAR sensor system can scana large area in the surrounding environment, even though the FOV of theLIDAR sensor system may be limited (i.e. with a narrow angle of view).

In accordance with various embodiments, the LIDAR sensor system can beused together with various types of sensors. For example, the LIDARsensor system can be used together with an inertial measurement unit(IMU)/Gyro/GPS for mapping the surrounding environment, by takingadvantage of various data fusion algorithms, such as the extended Kalmanfilter (EKF) algorithm. Additionally, the LIDAR sensor system can bemoved around for improving the detection of the surrounding environment.Also, the LIDAR sensor system can improve the detection of thesurrounding environment by acquiring more information (e.g., byaccumulating information over a period of time).

FIG. 23 shows an exemplary illustration of mounting a LIDAR sensorsystem on various movable platforms, in accordance with variousembodiments of the present invention.

As shown in FIG. 23(a), the LIDAR sensor system with one or morerotating prisms (e.g. a Risley prism pair or other optical elements) canbe mounted on a mounting platform, such as a moving vehicle that cancause a translational movement. For example, the mounting platform canbe aware of both its own position and movement. Also, the mountingplatform can be aware of the position and orientation (i.e. the angularposition) of each prism or each optical element.

Similarly, as shown in FIG. 22(b), the LIDAR sensor system with one ormore rotating prisms can be mounted on a rotating base. For example, themounting platform can be aware of both its own position and movement.Also, the mounting platform can be aware of the position and orientation(i.e. the angular position) of each prism or optical element.

Thus, the LIDAR sensor system can scan a moving area in the surroundingenvironment in a translational or rotational fashion.

FIG. 24 shows an exemplary illustration of using a LIDAR sensor systemto perform three dimensional scan, in accordance with variousembodiments of the present invention. As shown in FIG. 24(a), the LIDARsensor system can be carried by a two axis gimbal. Also as shown in FIG.24(b), a one axis gimbal can be used to carry the LIDAR sensor system.Alternatively, other types of gimbal can be used without limitation.

Combining with the rotation movement of the optical elements (such asthe Risley prisms) in the LIDAR sensor system and the rotationalmovement caused by the gimbal, the sensor system as shown in FIG. 24(a)or FIG. 24(b) can be used to direct the FOV (or angle of view) of theLIDAR sensor system to random directions in the three dimensional space.

In accordance with various embodiments, other approaches can be used forobtaining a large FOV (or angle of view). FIG. 25 shows an exemplaryillustration of combining multiple LIDAR sensor systems, in accordancewith various embodiments of the present invention. As shown in FIG. 25,multiple units of LIDAR sensor systems can be combined, with each unitfacing a different direction to achieve a larger combined FOV. Also,multiple units of LIDAR sensor systems can be arranged at differentpositions of the base/vehicle for achieving the same or similar effects.Additionally, multiple units of LIDAR sensor systems can be arrangedwith overlapped FOV to provide more point density within a specificangle range.

FIG. 26 shows a flowchart of scanning using a LIDAR sensor system, inaccordance with various embodiments of the present invention. As shownin FIG. 26, at step 2601, the LIDAR sensor system can generate a seriesof light pulses at different time points. At step 2602, the LIDAR sensorsystem can direct the series of light pulses toward a plurality ofoptical elements, each rotatable about an axis that is substantiallycommon. At step 2603, the LIDAR sensor system can control respectiverotation of each said optical element to collectively direct the seriesof light pulses to different directions in the angle of view.Furthermore, at step 2604, the LIDAR sensor system can acquire aplurality of target points, wherein each target point is detected basedon receiving at least a portion of photon energy of a said light pulsethat is reflected back from one or more objects in the angle of view.

Many features of the present invention can be performed in, using, orwith the assistance of hardware, software, firmware, or combinationsthereof. Consequently, features of the present invention may beimplemented using a processing system (e.g., including one or moreprocessors). Exemplary processors can include, without limitation, oneor more general purpose microprocessors (for example, single ormulti-core processors), application-specific integrated circuits,application-specific instruction-set processors, graphics processingunits, physics processing units, digital signal processing units,coprocessors, network processing units, audio processing units,encryption processing units, and the like.

Features of the present invention can be implemented in, using, or withthe assistance of a computer program product which is a storage medium(media) or computer readable medium (media) having instructions storedthereon/in which can be used to program a processing system to performany of the features presented herein. The storage medium can include,but is not limited to, any type of disk including floppy disks, opticaldiscs, DVD, CD-ROMs, microdrive, and magneto-optical disks, ROMs, RAMs,EPROMs, EEPROMs, DRAMs, VRAMs, flash memory devices, magnetic or opticalcards, nanosystems (including molecular memory ICs), or any type ofmedia or device suitable for storing instructions and/or data.

Stored on any one of the machine readable medium (media), features ofthe present invention can be incorporated in software and/or firmwarefor controlling the hardware of a processing system, and for enabling aprocessing system to interact with other mechanism utilizing the resultsof the present invention. Such software or firmware may include, but isnot limited to, application code, device drivers, operating systems andexecution environments/containers.

Features of the invention may also be implemented in hardware using, forexample, hardware components such as application specific integratedcircuits (ASICs) and field-programmable gate array (FPGA) devices.Implementation of the hardware state machine so as to perform thefunctions described herein will be apparent to persons skilled in therelevant art.

Additionally, the present invention may be conveniently implementedusing one or more conventional general purpose or specialized digitalcomputer, computing device, machine, or microprocessor, including one ormore processors, memory and/or computer readable storage mediaprogrammed according to the teachings of the present disclosure.Appropriate software coding can readily be prepared by skilledprogrammers based on the teachings of the present disclosure, as will beapparent to those skilled in the software art.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample, and not limitation. It will be apparent to persons skilled inthe relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.

The present invention has been described above with the aid offunctional building blocks illustrating the performance of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have often been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed. Any such alternate boundaries are thus withinthe scope and spirit of the invention.

The foregoing description of the present invention has been provided forthe purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed. Thebreadth and scope of the present invention should not be limited by anyof the above-described exemplary embodiments. Many modifications andvariations will be apparent to the practitioner skilled in the art. Themodifications and variations include any relevant combination of thedisclosed features. The embodiments were chosen and described in orderto best explain the principles of the invention and its practicalapplication, thereby enabling others skilled in the art to understandthe invention for various embodiments and with various modificationsthat are suited to the particular use contemplated. It is intended thatthe scope of the invention be defined by the following claims and theirequivalence.

What is claimed is:
 1. A sensor system, comprising: a light sourceconfigured to generate a light pulse directed along a first opticalpath; a reflective surface positioned to receive the light pulse fromthe light source and direct the light pulse along a second optical path;one or more optical elements positioned in an optical aperture toreceive the light pulse from the reflective surface, pass the lightpulse through the optical aperture, and direct the light pulse to one ormore objects in an angle of view of a sensor system; and a detectorpositioned to receive a portion of photon energy of the light pulse thatis reflected back from the one or more objects in the angle of view ofthe sensor system via the one or more optical elements and to convertthe received photon energy into one or more electrical signals, whereinthe reflective surface is offset from a center of the optical apertureto reduce blocking the light pulse that is reflected back from the oneor more objects.
 2. The system of claim 1, wherein the light pulseincludes a laser pulse.
 3. The system of claim 1, further comprising: acollimator positioned in the first optical path to collimate the lightpulse.
 4. The system of claim 1, wherein the one or more opticalelements include a prism, a mirror, a grating, an optical phased array,or a combination thereof.
 5. The system of claim 1, wherein the one ormore optical elements include a first optical element and a secondoptical element.
 6. The system of claim 5, wherein the first opticalelement and the second optical element are configured to rotateindependently about a generally common axis that corresponds to thesecond optical path.
 7. The system of claim 6, wherein the first opticalelement and the second optical element are configured to rotate atdifferent angular speeds.
 8. The system of claim 6, wherein the firstoptical element and the second optical element are configured to directthe light pulse to at least two different directions via rotating. 9.The system of claim 6, wherein the first optical element and the secondoptical element are configured to start rotation from different initialpositions.
 10. The system of claim 6, wherein at least one opticalelement is tilted relative to the common axis to reduce reflection ofincoming light from the light source into the detector.
 11. The systemof claim 6, further comprising: two motors, each positioned to controlan angular position or an angular velocity of a corresponding opticalelement.
 12. The system of claim 1, further comprising: a beam splitterarranged between the light source and the one or more optical elements,wherein the beam splitter is configured to direct the light pulse towardthe one or more of optical elements; and direct the photon energy of thelight pulse that is reflected back from the one or more objects towardthe detector.
 13. The system of claim 12, further comprising: a baffletube configured to extend a light exit on the beam splitter to preventscattered light of the light source from interfering with the detector.14. The system of claim 1, further comprising: an emitting structurearranged between the detector and the one or more optical elements,wherein the light source is positioned at one end of the emittingstructure and the reflective surface is positioned at an opposite end ofthe emitting structure.
 15. The system of claim 14, wherein the emittingstructure is configured to have a profile that matches a beam profile ofthe light pulse.
 16. The system of claim 1, wherein the detectorcomprises a receiving device that is configured with a profile thatmatches a beam profile of the light pulse.
 17. The system of claim 1,wherein each optical element includes a coating that reduces reflection.18. The system of claim 1, further comprising a band-pass filter thatmatches a wavelength of the light pulse.
 19. The system of claim 1,further comprising a spatial filtering apparatus configured to preventscattered or reflected light from reaching the detector, wherein thespatial filtering apparatus comprises at least one pinhole or slit thatmatches a beam profile of the light pulse.
 20. The system of claim 1,further comprising a field stop aperture that is arranged in front ofthe detector.
 21. The system of claim 1, wherein the sensor system isenclosed in a housing with an emission window.
 22. The system of claim1, wherein the light source, the reflective surface, the one or moreoptical elements, and the detector form a first unit, and wherein thesensor system further comprises at least a second unit, the second unitincluding a second light source, an additional one or more opticalelements, and a second detector.
 23. The system of claim 1, furthercomprising a vehicle, and wherein the vehicle carries the light source,the reflective surface, the one or more optical elements, and thedetector.
 24. The system of claim 1, further comprising a robot, andwherein the robot carries the light source, the reflective surface, theone or more optical elements, and the detector.
 25. A method of sensingobjects in an angle of view, comprising: generating, by a light source,a light pulse directed along a first optical path; directing, by areflective surface, the light pulse from the first optical path to asecond optical path toward one or more optical elements positioned in anoptical aperture such that the light pulse passes through the opticalaperture via the one or more optical elements, wherein the one or moreoptical elements are operable to direct the light pulse to one or moreobjects in the angle of view; receiving, via the one or more opticalelements, at least a portion of photon energy of the light pulse that isreflected back from the one or more objects in the angle of view,wherein the reflective surface is offset from a center of the opticalaperture to reduce blocking the light pulse that is reflected back fromthe one or more objects; and converting the received photon energy intoat least one electrical signal.
 26. The method of claim 25, furthercomprising: forming a light beam from multiple light pulses, wherein abeam profile of the light beam has a non-circular shape.
 27. The methodof claim 25, wherein the one or more optical elements includes a firstoptical element and a second optical element.
 28. The method of claim27, further comprising: rotating the first and second optical elementsabout a generally common axis that corresponds to the second opticalpath.
 29. The method of claim 27, further comprising: rotating the firstand second optical elements at different angular speeds.
 30. The methodof claim 27, further comprising: rotating the first and second opticalelements to produce a spiral pulse distribution in the angle of view.31. The method of claim 27, further comprising: rotating the first andsecond optical elements to produce a spiral pulse distribution in a formof a Lissajous figure.
 32. The method of claim 25, further comprising:measuring, based on the at least one electrical signal, a distancebetween the light source and one of the one or more objects in the angleof view.
 33. The method of claim 25, further comprising: generating,based on the at least one electrical signal, a point cloud correspondingto the one or more objects in the angle of view.